Field of the Invention
The present invention relates to a communication power amplifier intended mainly for satellite communication.
Background Art
Traveling wave tube amplifiers (TWTA) have been used so far as satellite communication power amplifiers, but TWTAs are being increasingly replaced by solid-sate amplifiers (SSPA) using FETs (field-effect transistors) such as GaAs (gallium arsenide) or GaN (gallium nitride) from the standpoints of cost and reliability in recent years. In power amplifiers, a low-frequency processing circuit is connected to an input matching circuit or an output matching circuit to provide high impedance at an operating frequency (fundamental frequency) and low impedance at a low frequency of the power amplifiers. In this way, the power amplifiers suppress intermodulation distortion while reducing influences of an RF signal on output power or efficiency. Conventional low-frequency processing circuits are made up of lines and capacitors connected to one another in series (e.g., see Japanese Patent Publication No. 2-61175).